In mobile satellite communication systems, the satellite is circularly polarized to overcome the effects of Faraday Rotation and to simplify polarization alignment at the ground terminal. The vehicle directive antenna must track the satellite under all the dynamic conditions of the host vehicle. In the case of a system employing a geostationary satellite, the elevation angle of the satellite subtended at the vehicle is a function of the latitude of the vehicle and the position of the satellite on the geostationary orbital arc. With the satellite optimumly located, the satellite elevation angles at vehicle latitudes of 70.degree., 45.degree. and 20.degree. North are about 10.degree., 45.degree. and 65.degree. respectively. The signal strength margins in geostationary mobile satellite communication systems are relatively small, and the coverage must be sufficiently high to maintain good communications.
One such antenna is described in U.S. patent 4,700,186 issued Oct. 13th, 1987, invented by R. Milne. The antenna is elegantly simple, inexpensive to manufacture and has negligible RF loss. It generates, electronically, a number of fixed beams in azimuth and elevation and is designed to meet the requirements of mobile satellite communications systems providing regional coverage i.e. the North American continent. The antenna is however linearly polarized and there is a nominal 3 dB loss in gain when operating with a circularly polarized satellite. There is a requirement, in global mobile satellite communication systems, for higher antenna gain. A polarized lens structure has been invented that converts the linearly polarized signal radiated by the antenna to circular polarization and extends the elevation angular coverage.